Ceramic air-cavity and plastic air-cavity/overmold packages are widely used for RF/microwave discrete power transistors. Both types of packages provide a reliable and easy-to-handle handle mechanical design. However, ceramic air-cavity and plastic air-cavity/overmold packages are difficult to design in an electrical sense due to their stack-up and predetermined physical dimensions.
RF transistors are commonly packaged with input and output matching networks. These input and output matching networks are typically provided by discrete reactive components, i.e., capacitors and inductors. For example, an output matching network for an RF transistor may be provided from a discrete capacitor that is mounted to the package substrate. The RF transistor is connected to the capacitor by inductive bond wires. The parameters of the output matching network can be tailored to match the output impedance of the packaged device to a fixed value (e.g., 50 ohms). In a ceramic open cavity RF package, one common approach for the output matching network is a high pass topology, which is designed to propagate higher frequency signals and to shunt lower frequency signals.
Parasitic capacitances, inductances, and resistances in the conventional input/output matching network configurations described above detrimentally impact the performance and/or power consumption of the packaged RF device. These parasitic effects are attributed to mutual inductance and capacitive coupling between the bond wires and the associated bond pads. High-frequency effects also influence the behavior of the input/output matching network. The physical arrangement of the bond wires can be altered to mitigate these phenomena, but only with limited success.